To improve performance of advanced communication systems, various research institutions and standardization groups provide various technologies. For example, recent attention focuses on a multi-carrier modulation scheme Orthogonal Frequency Division Multiplexing (OFDM) which transmits data by dividing a frequency band of high data rate into a plurality of orthogonal subcarriers.
Meanwhile, a wireless communication system has a cell structure for the sake of efficient system configuration. The cell indicates is a subdivided area to efficiently utilize the frequency. In general, a base station is installed at the center of the cell to relay a terminal, and the cell indicates service coverage provided by one base station.
When neighboring cells of the OFDM/OFDMA system use the same subcarrier in a multi-cell environment, this can cause interference to users. This is referred to as inter-cell interference. Particularly, the inter-cell interference becomes a great problem to the terminal near a cell boundary. In downlink, the terminal in the cell boundary is greatly interfered by the neighboring cell. In uplink, the terminal in the cell boundary not only imposes strong interference on the neighboring cell but also suffers from the low data rate due to path loss in a serving cell.
To mitigate the inter-cell interference, the neighboring cells can use different subcarriers. However, radio resources usable by one base station reduce.
Alternatively, a multi-cell cooperative scheme is suggested to reduce the inter-cell interference in the multi-cell environment. The multi-cell cooperative scheme can enhance communication performance of the terminal near the cell boundary. The multi-cell cooperative scheme is performed based on one cluster or cloud including a plurality of cells. Each cluster or the cloud is controlled by a central unit.
FIG. 1 depicts conventional clusters.
Referring to FIG. 1, multiple cells are grouped to form one cluster, and a wireless communication system includes a plurality of clusters.
A Central Unit (CU) of each cluster dynamically determines whether to transmit data of the cells in the cluster per Transmission Time Interval (TTI), and aborts the transmission of other cell when one cell transmits data so as to control the inter-cell interference in the cluster. Hereafter, an interval where the other cell does not transmit data is referred to as a blank, and the blank of the cells in the cluster is referred to as a blank pattern. That is, the CU determines the blank of the cells of the most adequate cluster per TTI using channel condition of all of the terminals in the cluster. Each cell in the cluster performs scheduling using the blanks of the cell and the neighboring cells and the channel condition.
The number of the cells controlled by one CU is limited. That is, the whole system cannot be grouped into a single cluster and accordingly is divided into the multiple clusters. In this regard, a method for controlling inter-cluster interference using the inter-cluster distributed cooperation is required.